Android Bootmeth

Android provides a mechanism for booting its Operating System from eMMC storage, described on source.android.com.

Android has strong requirements about partitioning layout which are described here. Because multiple partitions are required, this bootmeth only operates on whole mmc devices which have a valid partition table.

When invoked on a bootdev, this bootmeth searches for the misc partition in order to read the boot mode, which can be one of following:

Normal

Boot the regular Android Operating System.

Recovery

Boot a slimmed down Recovery Operating System. Can be used to factory reset the device or to apply system updates.

Bootloader

Stay in U-Boot and wait for fastboot commands from the host.

After the boot mode has been determined, this bootmeth will read the slot suffix from the misc partition. For details about slots, see the AOSP documentation.

When both the boot mode and the slot suffix are known, the bootflow is created.

When the bootflow is booted, the bootmeth reads the kernel, the boot arguments and the vendor ramdisk. It then boots the kernel using bootm. The relevant devicetree blob is extracted from the boot partition based on the adtb_idx environment variable.

The compatible string “u-boot,android” is used for the driver. It is present if CONFIG_BOOTMETH_ANDROID is enabled.